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  <title>Release Notes &raquo; Release 2.2.0 (2019/06/15) | Taskflow QuickStart</title>
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        <h1>
          <span class="m-breadcrumb"><a href="Releases.html">Release Notes</a> &raquo;</span>
          Release 2.2.0 (2019/06/15)
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          <h3>Contents</h3>
          <ul>
            <li><a href="#release-2-2-0_download">Download</a></li>
            <li><a href="#release-2-2-0_new_features">New Features</a></li>
            <li><a href="#release-2-2-0_breaks_and_deprecated_features">Breaks and Deprecated Features</a></li>
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<p>Cpp-Taskflow 2.2.0 is the 3rd release in the 2.x line! This release includes several new changes such as tf::ExecutorObserverInterface, tf::Executor, isolation of taskflow graph and executor, benchmarks, and so forth. In particular, this release improve the performance of the work stealing scheduler.</p><section id="release-2-2-0_download"><h2><a href="#release-2-2-0_download">Download</a></h2><p>Cpp-Taskflow 2.2.0 can be downloaded from <a href="https://github.com/cpp-taskflow/cpp-taskflow/releases/tag/v2.2.0">here</a>.</p></section><section id="release-2-2-0_new_features"><h2><a href="#release-2-2-0_new_features">New Features</a></h2><ul><li>A new executor class to isolate the execution module from a taskflow</li><li>A new observer interface to inspect the activities of an executor</li><li>A decomposable taskflow construction interface</li><li>A new work-stealing algorithm to improve the performance</li></ul></section><section id="release-2-2-0_breaks_and_deprecated_features"><h2><a href="#release-2-2-0_breaks_and_deprecated_features">Breaks and Deprecated Features</a></h2><p>In this release, we isolated the executor interface from <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a>, and merge tf::Framework with <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a>. This change largely improved the modularity and composability of Cpp-Taskflow in creating clean task dependency graphs and execution flows. Performance is also better. While this introduced some breaks in <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a>, we have managed to make it as less painful as possible for users to adapt to the new change.</p><p>Previously, <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a> is a hero class that manages both a task dependency graph and the execution of all graphs including frameworks. For example:</p><pre class="m-code"><span class="c1">// before v2.2.0, tf::Taskflow manages both graph and execution</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Taskflow</span><span class="w"> </span><span class="nf">taskflow</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span><span class="w">  </span><span class="c1">// create a taskflow object with 4 threads</span>
<span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([]</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;task A</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">;</span><span class="w"> </span><span class="p">});</span>
<span class="n">taskflow</span><span class="p">.</span><span class="n">wait_for_all</span><span class="p">();</span><span class="w">   </span><span class="c1">// dispatch the present graph</span>

<span class="n">tf</span><span class="o">::</span><span class="n">Framework</span><span class="w"> </span><span class="n">framework</span><span class="p">;</span><span class="w">   </span><span class="c1">// create a framework object</span>
<span class="n">framework</span><span class="p">.</span><span class="n">emplace</span><span class="p">([]</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;task B</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">;</span><span class="w"> </span><span class="p">});</span>
<span class="n">taskflow</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">framework</span><span class="p">);</span><span class="w">   </span><span class="c1">// run the framework once</span>
<span class="n">taskflow</span><span class="p">.</span><span class="n">wait_for_all</span><span class="p">();</span><span class="w">   </span><span class="c1">// wait until the framework finishes</span></pre><p>However, this design is awkward in many aspects. For instance, calling <code>wait_for_all</code> dispatches the present graph and the graph vanishes when the execution completes. To reuse a graph, users have to create another special graph called framework and mix its execution with the one in a taskflow object. Given the user feedback and lessons we have learned so far, we decided to isolate the executor interface out of <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a> and merge tf::Framework with <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a>. All execution methods such as <code>dispatch</code> and <code>wait_for_all</code> have been moved from <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a> to tf::Executor.</p><pre class="m-code"><span class="c1">// starting from v2.2.0, tf::Executor manages the execution of graphs</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Taskflow</span><span class="w"> </span><span class="n">taskflow</span><span class="p">;</span><span class="w">      </span><span class="c1">// create a taskflow to build dependent tasks</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([]</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;task A</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">;</span><span class="w"> </span><span class="p">});</span>
<span class="n">tf</span><span class="o">::</span><span class="n">Task</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace</span><span class="p">([]</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o">&lt;&lt;</span><span class="w"> </span><span class="s">&quot;task B</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">;</span><span class="w"> </span><span class="p">});</span>
<span class="n">A</span><span class="p">.</span><span class="n">precede</span><span class="p">(</span><span class="n">B</span><span class="p">);</span>

<span class="n">tf</span><span class="o">::</span><span class="n">Executor</span><span class="w"> </span><span class="nf">executor</span><span class="p">(</span><span class="mi">4</span><span class="p">);</span><span class="w">   </span><span class="c1">// create an executor of 4 threads</span>
<span class="n">executor</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">taskflow</span><span class="p">);</span><span class="w">     </span><span class="c1">// run the taskflow once</span>
<span class="n">executor</span><span class="p">.</span><span class="n">run</span><span class="p">(</span><span class="n">taskflow</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">);</span><span class="w">  </span><span class="c1">// run the taskflow twice</span>
<span class="n">executor</span><span class="p">.</span><span class="n">wait_for_all</span><span class="p">();</span><span class="w">    </span><span class="c1">// wait for the three runs to finish</span></pre><p>The new design has a clean separation between a task dependency graph builder <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a> and the execution of graphs tf::Executor. Users are fully responsible for the lifetime of a taskflow, and need to ensure a taskflow is alive during its execution. Besides, all task constructs remain unchanged in <a href="classtf_1_1Taskflow.html" class="m-doc">tf::<wbr />Taskflow</a>. In most situations, you will just need to add an executor to your program to run your taskflow graphs.</p><p>Again, we apologize this breaking change! I hope you can understand what we did is to make Cpp-Taskflow provide good performance scaling and user experience.</p></section>
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